Hong Kong's Chief Executive Carrie Lam (C) visits the Kowloon Masjid and Islamic Centre in Tsim Sha Tsui to meet with representatives of the Incorporated Trustees of the Islamic Community Fund of Hong Kong and other leaders of the local Muslim community, in Hong Kong, China Oct 21, 2019. REUTERS

Municipal workers scrubbed away noxious blue dye from the steps of Hong Kong's biggest mosque on Monday, while Muslim worshippers expressed frustration over police firing a water cannon outside the mosque during a large anti-government march. Senior police officers visited the Kowloon mosque to explain it was hit accidentally during Sunday's clashes with demonstrators, and Hong Kong's leader Carrie Lam met with community leaders on Monday to apologise.

"It was unnecessary to drag this place of worship into this conflict between the government and the people," Arabi Mohideen, 60, said after attending dawn prayers at the mosque in the bustling Tsim Sha Tsui district.

During protests in Kowloon on Sunday, a police water cannon truck shot bursts of blue-dyed water at a small clutch of people on the footpath outside the mosque, hitting its gate and steps.

Protesters, some clad in black and masked, arrived soon afterward to help clean up. They coughed uncontrollably while wiping down metal railings and the gate, as the dye was mixed with an irritant designed to force crowds to disperse more quickly.

Police, already facing criticism for heavy-handed tactics, issued a statement saying the incident was "most unfortunate" and unintended, while senior officers went to meet Muslim leaders late at night to offer apologies.

Lam's apology on Monday further underscored the sensitivity, and was accepted by worshippers, who lamented being caught up in the unrest.

"It's a symbol of peace," said Waqar Haider, an interpreter for South Asian residents and worshipper at the mosque. "It shouldn't have happened...South Asians have not been involved in any protesting — anti-Hong Kong or pro-Hong Kong. We're just living peacefully."

South Asians, who hail from Pakistan, India, Nepal and Bangladesh, comprise about 1% of Hong Kong's population, according to 2016 census figures.

The community is concentrated around the mosque and the nearby Chungking Mansions building, a ramshackle collection of restaurants, cheap hotels and South-Asian run stores.

There had been concerns over the past week that the South Asian community could suffer some backlash from some pro-democracy factions after a prominent rights activist was beaten up last week by assailants described by police as "non-Chinese".

Criminal gangs, or triads, in the city, have sometimes hire non-Chinese, including South Asians to carry out attacks on individuals.

Consequently, the Muslim community had been on edge ahead of Sunday's protest march, which wound past the mosque, though protesters had promised to pass by peacefully. Instead it was the police action that caused offence. Acknowledging the upset caused to its community, the Muslim Council of Hong Kong called on people to leave their rancour behind.

"May Allah bring ease to all such tense situations," the council wrote on its Facebook page. "Guide us to do what's best for the community and make us people who look to defuse the situation and not incite it further."